With recent polls in the heavily Mormon state showing a decisive swing to McMullin, Trump used an appearance on Fox News to dismiss the independent candidate as "a puppet" being manipulated by The Weekly Standard editor Bill Kristol—a "Never Trump" Republican who has tried for months to field an independent candidate to take on the GOP nominee.

The remark drew a blistering response from McMullin on Twitter, who excoriated Trump as an "authoritarian" and a "big government liberal."

Trump's broadside against the independent McMullin comes as the real estate mogul is jockeying for advantage in a contest where his Democratic challenger holds the poll position, but the election still remains competitive.

Few people think McMullin has an actual path to the Oval Office, given that he's failed to make the ballot in all 50 states, lacks party backing and launched his candidacy late in the cycle. That said, he's emerged as an alternative for conservative Republicans that remain hesitant to cast a vote for Trump or former Secretary of State Hillary Clinton.